Semiconductor devices are continuously increasing in performance, and at the same time are generating increasing amounts of excess heat during operation. As individual devices are continually reduced in size, with more heat generated in a shrinking area, the problem of heat dissipation has become a critical factor affecting device performance.
In order to effectively cool a device chip, a heat spreader chip is typically attached to the backside of the device chip. FIG. 1 shows a conventional arrangement of a semiconductor module, where a device chip 1 (having the actual devices fabricated in region 1 a near its front surface) is turned face down and electrically connected to a substrate 2; a number of C4 connectors 3 (controlled-collapse chip connectors) form the interconnects between the devices and the substrate. A layer 4 of heat-conducting material is applied to the backside 1b of device chip 1; this layer serves to attach heat spreader chip 5 to the device chip. A shown in FIG. 1, heat spreader chip 5 is typically larger than device chip 1. A conventional material for heat spreader chip 5 is SiC.
A conventional material used in layer 4 to attach the heat spreader to the chip is thermal paste. The thermal paste layer is typically 50–100 μm thick. The thermal conductance of thermal paste is at best 0.05 W/cm° C., which does not allow for efficient heat transfer from the chip to the heat spreader. Solder has been used as an alternative material for layer 4; solder has better thermal conductance than thermal paste (about 0.2 W/cm° C.), but has physical properties that make it unattractive for this purpose in device processing. There is a need for a method and structure for attaching a heat spreader chip to a device chip, in which the attachment layer 4 has significantly higher thermal conductance than thermal paste. In addition, it is desirable that fabrication of such an attachment layer, and bonding of the heat spreader and device chip, be easily integrated into conventional device manufacturing processes.